1. Field of the Invention
The present invention relates to a component carrier tray, and more particularly a hybrid carrier tray for high temperature applications.
2. Description of the Related Art
Prefabricated components and chips lie at the heart of most anialog and digital circuits. As these circuits become more prevalent and more complex, it has become increasingly important to those who manufacture and sell the component parts, as well as to those who purchase components and implement circuits using them, that these often delicate or sensitive components can be inspected efficiently and effectively, shipped securely, and handled easily during formation and installation. Similar demands exist with respect to other electrical and mechanical components.
Component manufacturers traditionally handle their parts during production in various forms of transport packaging, one of the most popular being waffle trays. In waffle trays, each tray is formed with a series of depressions or pockets formed in a grid pattern. A component part is inserted into a pocket and transported therein. This system provides an efficient arrangement in which the components can be stored or manipulated by an automated assembly process.
In order to facilitate the handling of these carrier trays, the Joint Electronic Device Engineering Council (JEDEC) has promulgated standards for size and shape. JEDEC standards dictate the form of such exterior features as end tabs for machine manipulation and complementary top and bottom features for stacking.
In addition to facilitating handling of the carrier, it is important in automated production lines to ensure that the components remain oriented properly within the carrier. This permits the machinery to determine the location and orientation of particular components with sufficient accuracy. In addition, the leads of the components are often quite delicate, and therefore susceptible to damage during formation, shipping and storage. Accordingly, it is beneficial to form pockets with interior features, well known in the art, designed to orient and protect the component from being bounced against the interior surfaces of the pocket.
In order to form trays with exterior features meeting JEDEC standards and interior pocket features that will adequately accommodate the components therein, trays are usually injection molded of a thermoplastic resin that is substantially amorphous (rather than crystalline or semi-crystalline) such as polyether sulfone. However, it is our experience that these materials generally do not fare well when exposed to temperatures at or above approximately 200.degree. C. It is becoming common for manufacturers to subject the components to those temperatures and even higher temperatures, often about 250.degree. C., in processes such as "infrared reflow" processing or convection heating to solder connector pins to ball grid array components, or "baking" to remove potentially-damaging trapped moisture from components prior to installation processes. This means that the components must often be removed from the trays before the components can be subjected to such high-temperature processes. It would greatly facilitate the handling of the components if the trays in which they are handled could withstand the higher temperatures encountered in such processes. One thermoplastic of which the present applicants are aware, TORLON.RTM. (Amoco), a poly(amide-imide) resin, does exhibit favorable high temperature characteristics. However, it is our experience that the grades of TORLON.RTM. that are suitable for use in carrier trays are relatively difficult and time-consuming to mold, and therefore pot particularly well suited to use in component carrier manufacture.
U.S. Pat. No. 5,428,100, to Asai et al., relates to a resin composition intended for use in molded articles such as temperature-resistant trays for integrated circuits or the like. This patent discusses liquid crystal polyesters (LCPs) having various temperature characteristics, some of which would seem to be useful in the high-temperature processes discussed above.
As recognized in the Asai patent, LCP resins can be very difficult to injection mold. It has been our experience that this is also true for other high-temperature "semi-crystalline" materials, such as thermoset polyimide (TPI) resins, polyester ether ketone (PEEK) resins, and polyphthalamide (PPA) resins. These materials have highly ordered molecular structures that contribute to relatively high, sharply defined melt points. However, the molecular orientation of these materials also causes anisotropic shrinkage--shrinking more in the direction transverse to the melt flow than in the direction of the melt flow--as they set during injection molding, leading to unpredictable warpage and/or residual internal stresses. Thus, it can be very difficult to produce relatively large, flat carrier trays from such materials. Further, even if the tray can be formed flat, once it is subjected to high processing temperatures, the residual stresses can relax and cause the tray to flex unpredictably. For example, tests were performed on trays formed of a modified PPA, each having an overall length of approximately 323 mm, an overall width of approximately 136 mm, and an external thickness of approximately 12 mm. When exposed to temperatures of just 150.degree. C. for 24 to 48 hours, the trays would ware unacceptably, with changes in length and width of approximately 0.4 and 0.3 mm, respectively.
The Asai patent proposes a specific material composition to overcome this problem. Examples 10 and 16 of the Asai patent, for example, assert that IC trays molded out of the disclosed LCP exhibit relatively low degrees of warpage in formation add after prolonged exposure to temperatures of 240.degree. C. It would be preferable, however, to be able to produce trays possessed of such properties using any of a variety of widely available molding resins, not just the particular LCP disclosed in the Asai patent.
An alternate approach to that of the Asai patent is to form the trays out of aluminum, steel or other metal. However, in order to form metallic trays with detailed exterior and interior features, they generally have to be machined, greatly increasing the cost of production. Unfortunately, casting metal trays presents similar warpage problems to those encountered in the injection-molding of trays from semi-crystalline resins.
It is known in the art to produce component transport devices that are made of more than one material. For example, U.S. Pat. No. 5,131,535, to O'Connor et al., relates to an electrical device transport medium made of two different materials. A plurality of plastic carrier unit inserts are held in a generally planar relationship by a metallic frame. The carrier units are preferably formed of graphite loaded polyether sulfone, which according to the patent is capable of enduring all the heating and cooling chambers ("soak chambers") through which the electrical devices must pass. The carrier units are latchable into a coordinate matrix of carrier unit holes defined by the frame, and are permitted a small amount of play in a direction perpendicular to the plane of the frame, i.e., in an up-and-down direction. The frame and carrier units are disposed on a bi-level process machine platform during pre-shipment "backend processing." However, the O'Connor patent does not recognize or address the problems associated with processes in which temperatures reach the ranges being considered here (it being our understanding that soak chamber temperatures are not normally higher than about 150.degree. C.).
Another example of a hybrid tray is U.S. Pat. No. 5,547,082, to Royer et al., which discloses a component tray frame with a removable insert that is releasably secured to the frame. The insert has a plurality of pockets for storing the components. The frame is preferably formed of a polymeric material that is thermoset or thermoplastically formed, e.g., polyether sulfone (the traditional tray polymer), or PEEK or TPI (semi-crystalline resins). Metals such as steel and aluminum are also suggested. As for the inserts, those are preferably made of a polymeric material that is adapted to withstand temperatures of approximately 125.degree. C. for periods in excess of 24 hours. Specifically mentioned is polyether sulfone, but not PEEK or TPI. The Royer patent does not recognize the problems encountered in utilizing trays at a temperature of 200.degree. C. or higher.
Therefore, there is a need in the art for a relatively low-cost component carrier tray that can withstand temperatures encountered in high-temperature component processing.
There is a further need for such a carrier that can be formed consistently without unacceptable levels of warpage.
There is yet another need for such a carrier with pockets that can include fine interior features to protect the component held therein.
There is a further need for such a carrier that can include standardized exterior features to facilitate machine handling and/or stacking.